165 mm cranks?

[jpw]

I see Campagnolo and Shimano make 165 mm cranks for their top end groups.

What saddle height range would make 165 mm cranks beneficial?

[classtimesailer]

My next pair of cranks will be 165s. My saddle height is 77-78. Think clearance in turns.

[rice rocket]

Triathletes use 165mm cranks too b/c it lets them tuck more w/o your knees hitting your chest.

[11.4]

Some will probably flame me for this, but I say not to change your saddle height. It's the center of your pedal rotation that matters, not your maximal extension. If you go to shorter cranks, you don't extend quite so far and you don't raise quite so far, but the radius is the only thing that changes -- your rotation is still around the same center your body is used to.

Five millimeters or so doesn't do that much to ground clearance, and that argument harkens back to all the old arguments for high bottom brackets as well -- the way to do turns is to enter on the right line, know how to turn, and coast the tightest part.

Short cranks reduce the intrusion of your quads into your diaphragm (or gut, if your gut is more in the way) so your body can pedal more efficiently and without breathing impairment. They limit the range of flexion of the knee joint, which for some people is useful in preventing joint problems. They also limit fore and aft position of your foot, which in turn alters the angle of attack of your knee joint (think KOPS if you want to believe in that malarkey). They may help you spin faster, but frankly, plenty of professional track sprinters are riding longer cranks and spinning just fine -- I think that argument is fading into happy oblivion. Short cranks, with the same center of rotation, will allow you to optimize saddle position fore and aft to get the best use of your flutes, and can give you a more open hip position so you can use your quads more effectively as well -- not big improvements, but enough to matter.

But mostly, it comes down to winning (I think racing, because that is what I coach, and it's a good metric for anyone). You're into this to ride fast (that IS why you just got that bling Dave Kirk frame, right?). I've read all the scientific and medical literature and frankly, nobody really understands what is going on with an individual rider. There are general guidelines, yes. But the last five millimeters or the last degree or two of angle? Our bodies adapt to different positions and mostly we just try to avoid position-induced injuries and then try to pay attention to a few basic and pretty obvious metrics. But we've all seen major pro cyclists win with dramatically different styles and positions. There are a lot of things that go into a winning ride, and KOPS or crank length aren't that critical. I ride 165's because I'm short and with that crank length I'm injury free, and I race mostly on the track and have ridden 165's for years. None of those are particularly valid arguments for not changing to 170's; it's more relevant that I don't want to spend the money on an experiment to see if 170's will work better. Or 172.5's. Or 175's. I do know that it probably won't improve matters and may induce problems. If I want to do better, I make myself faster, and I do that by improving fitness and strength and all the other components of winning. It's escapist to believe that changing crank arm length will make me win if I'm not putting the effort into actually making myself faster.

Apologies for the diatribe. I like short cranks and narrow handlebars and very low racing positions (aka slammed stems most of the time). But I know it's my legs and my lungs that determine whether I win. I wish it were otherwise, but that would be a con.

[giordana93]

Easier to spin

Better cornering clearance

Easier on the knees for some (less acute angles at top of stroke; minimizes desire to grind a big gear)

Pretty common on the track


That said, if you have really long legs and feet, it prolly would not feel right.

My favorite analogy for crank length is the height of steps on stairs. Too tall or too short both feel wrong, and you either have to do many steps fast or big huge strides that stress.

And it's not about leverage--that argument drives me crazy. The whole gear system from crank length, chainring, cog, and rear wheel diameter is part of the leverage package. With other variables equal, a longer crank is simply an easier gear. Normally that would lead to faster cadence, but longer cranks are harder to spin so people shift up and pedal more slowly. Lots of people prefer that slow grinding pedal stroke to a well-tuned higher cadence, but then some people are more natural spinners or grinders. Neither is wrong, just preference. You can guess which one I am. 165s and 170s on road, 175 on mtb for grinding up climbs and hopping logs. Short 80cm inseam fwiw.

Oh, 165 popular for fixed gear on road too, from track influence and inability to coast thru corners.

[R2D2]

Track

[witcombusa]

I run all different crankarm lengths on various bikes.
From 165mm on a road fixed gear bike up to 175mm on a loaded touring mount. Plenty of 170's and 172.5's in the mix as well.

Honestly, after the first mile or two you don't even notice, even when coming right off something different.

5mm is nothing, less than a quarter of an inch!

[Sheldon4209]

I rode 175mm on my tandem because they came on it. A few years later I went to 170mm and my stoker/wife could tell the difference. She says that my pedal stoke is smoother with the shorter cranks. I have an 81 cm pbh.

[ultraman6970]

IMO it depends a lot of the person, some guys cant tell, other ones notice right away, in my particular case I used 175 like for a month and eventhought I moved the saddle to account for the difference I was not able to spin too good so I ended up selling them.

[BdaGhisallo]

I am pondering this for myself. I am currently on 170mm arms and have been for about four years. For the twenty years previous I was on 172.5mm, since that was the length on the Trek I bought when I was fifteen.

Thinking about this and how femur and tibia length factor into inseam length, and how the leg moves mechanically, wouldn't optimal crank length (for fit and pedaling mechanics) be better related to tibia length?

Wouldn't a higher femur to tibia ratio see less closing of the hip angle over the course of the pedal stroke than with a lower ratio, and minimize the intrusion of the quad into the diaphragm and gut, as 11.4 put it? If one has longer tibias, would that intrusion be limited more by a move to a shorter crank arm, absent other changes, than if one had long femurs and short tibias for a given inseam?

[R2D2]

I am pondering this for myself. I am currently on 170mm arms and have been for about four years. For the twenty years previous I was on 172.5mm, since that was the length on the Trek I bought when I was fifteen.

Thinking about this and how femur and tibia length factor into inseam length, and how the leg moves mechanically, wouldn't optimal crank length (for fit and pedaling mechanics) be better related to tibia length?

Wouldn't a higher femur to tibia ratio see less closing of the hip angle over the course of the pedal stroke than with a lower ratio, and minimize the intrusion of the quad into the diaphragm and gut, as 11.4 put it? If one has longer tibias, would that intrusion be limited more by a move to a shorter crank arm, absent other changes, than if one had long femurs and short tibias for a given inseam?

Peter White has an article on this.
You'll need to decide whether you agree or if it's useful.
http://www.peterwhitecycles.com/fitting.htm

[christian]

I think you guys are overthinking this.

What saddle height range would make 165 mm cranks beneficial?A low one, for short people. Say <680mm from the center of the bb.

[Ralph]

Other than having cranks that are too long for you, I don't see how crank length matters much...as least from the normal choice we have.
I'm 5' 10", and still ride 170's on my bikes with 52 ring. Some say if I went to longer cranks, I could get more "leverage". But as I remember from physics....you can make the lever (crank arm) longer or the pully (chainring) smaller. With same result. 170 compared to 172.5 and 53 compared to 52, about same leverage. As said above, ride what gives you results.....as long as it's not too long.

[11.4]

I am pondering this for myself. I am currently on 170mm arms and have been for about four years. For the twenty years previous I was on 172.5mm, since that was the length on the Trek I bought when I was fifteen.

Thinking about this and how femur and tibia length factor into inseam length, and how the leg moves mechanically, wouldn't optimal crank length (for fit and pedaling mechanics) be better related to tibia length?

Wouldn't a higher femur to tibia ratio see less closing of the hip angle over the course of the pedal stroke than with a lower ratio, and minimize the intrusion of the quad into the diaphragm and gut, as 11.4 put it? If one has longer tibias, would that intrusion be limited more by a move to a shorter crank arm, absent other changes, than if one had long femurs and short tibias for a given inseam?

Actually, I think it's the other way around. Think about your cranks rotating. What do your tibia do? They are consistently more or less vertical and thus establish the maximum reach to the bottom of your pedal stroke. In other words, tibia length determines saddle height.

Now think about your femur. It goes from nearly horizontal to nearly vertical. That is what determines how much your quads press up into your chest. Put another way, femur length is what determines how much of a diameter your pedal stroke can make, i.e., what length crankarms you can use.

Long femurs plus long tibia give the ideal combination -- long tibia let you set a high saddle so you have room for a crank rotation to accommodate your long femurs. Long tibia and short femurs aren't quite as good but at least the long tibia give you saddle height to keep your thighs out of the way, and your range of pedal motion will be less anyway. If you have short tibia and long femurs, well, ... it might be time to try synchronized swimming. In this case, you can't set your saddle particularly high but your pedal rotation is in a big circle, so you are alternately stretching at the bottom of the stroke and reaching up into your abdomen and chest at the top of the stroke. Your femurs are forcing a large pedal rotation circle which you can only slightly mitigate with crankarm length.

This is all why some riders feel crankarm length differences, and others don't. If the tibia to femur length ratio varies, it changes the circle your leg is going to turn, regardless of whatever crank arms you install. It determines those who are genetically predisposed to cycling. It highlights some of the fitting issues that are usually overlooked in framebuilding and in fitting -- fitters worry about where your knee is in relation to the pedal (without necessarily considering whether a short femur pulls your whole butt forward to compensate in this method and thereby creates bigger problems) or about knee angle at bottom of stroke (without necessarily considering that you have to make a circle with your feet and working from only one side of the circle will ignore the rest of the circle). There's a whole new school of bike fitting that's needed here. I've coached it for years on the track and the riders using it have done well. Power readings, such as they are worth, are consistent. Mostly, riders win more and that's the best metric in the end.

Hope that helps.

[bargainguy]

I'm a shorty at 5'4 and a spinner with short legs. Out of curiousity, I wanted to see what would happen with a really short crank. The usual disclaimers here: YMMV, ask your doctor or bike fitter, etc.

So I experimented with a 170mm Ultegra triple shortened to 148mm. I wanted to see how this worked on a high-end folder (Bike Friday Air Glide), whether the added benefit from easier spinning resulted in any obvious changes otherwise. BTW, some folding bike owners intentionally run short cranks to make packing in a case easier, but I wanted to go a little more extreme than 165.

After riding the 148 for a couple years, I went back to an identical Ultegra 170 triple and removed the 148. The 148 was great for spinning, but as soon as I hit a hill or stiff wind, noticeably less "punch." Gearing up didn't help, I just didn't seem to be making as much headway. It was a little easier to pack the bike in a case with the 148, tho.

My legs were moving smaller circles but subjectively, the effort needed against wind or hills increased greatly compared to the 170. I didn't change a single thing to the bike during that 2-yr test other than the crank so no other variables to contend with.

So I'm back to 165 on some bikes and 170 on others. I don't notice the 5mm difference as much as the 148/170 difference.

[BdaGhisallo]

Now think about your femur. It goes from nearly horizontal to nearly vertical. That is what determines how much your quads press up into your chest. Put another way, femur length is what determines how much of a diameter your pedal stroke can make, i.e., what length crankarms you can use.

Long femurs plus long tibia give the ideal combination -- long tibia let you set a high saddle so you have room for a crank rotation to accommodate your long femurs. Long tibia and short femurs aren't quite as good but at least the long tibia give you saddle height to keep your thighs out of the way, and your range of pedal motion will be less anyway. If you have short tibia and long femurs, well, ... it might be time to try synchronized swimming.

I have always heard the opposite. For a given leg length, that it is optimal to have a high femur:tibia ratio. I've read that the general population average is 1.1 and some riders like Hinault, Moser and LeMond had ratios approaching 1.19. Their relatively longer femurs were a biomechanical advantage, and also afforded them the capacity to handle a greater amount of saddle setback. Something about greater leverage with the longer femurs.

[11.4]

I have always heard the opposite. For a given leg length, that it is optimal to have a high femur:tibia ratio. I've read that the general population average is 1.1 and some riders like Hinault, Moser and LeMond had ratios approaching 1.19. Their relatively longer femurs were a biomechanical advantage, and also afforded them the capacity to handle a greater amount of saddle setback. Something about greater leverage with the longer femurs.

Long femurs relative to total body size definitely are important. The tibia is pretty much just along for the ride (pardon the pun) -- it goes up and down but doesn't contribute that much and its length is rather irrelevant to power output. It's about femur length to total body size that predisposes one to being a champion. However, after that, if your tibia is short relative to your femur, it limits your total saddle height and thus limits your crankarm length.

You are right. So am I. You just cited the relationship between femur and body. That some riders have femurs longer than tibias is secondary to having long femurs relative to body size. The long femur gives you the setback you describe regardless of whether your tibia is long or short. But if the tibia is short, you can't get as much overall extension and thus you have to sit lower relative to your pedal position.